1. Field of the Invention
The present invention relates to a method of inhibiting adhesion of a by-product inside a duct, the method being effectively employed in a waste gas treatment wherein waste gas which contains poisonous gas components such as SO.sub.x and/or NO.sub.x and which has ammonia added thereto is irradiated with electron beams to change these poisonous gas components into by-products which are useful as fertilizers, e.g., ammonium sulfate and ammonium nitrate.
2. Description of the Prior Art
It has heretofore been known to treat waste gas which contains poisonous gas components such as SO.sub.x and/or NO.sub.x by adding ammonia to the waste gas, irradiating this waste gas with electron beams to thereby change the poisonous gas components into ammonium sulfate and/or ammonium nitrate, and collecting the resulting by-product.
FIG. 1 illustrates a typical flow sheet and apparatus of a commercial plant to which the above-described conventional method for treating waste gas is applied. Waste gas which is generated from a boiler 1 is allowed to cool down to, in general, about 150.degree. C. and this gas is sprayed with cooling water 4 in a cooling tower 3 so that the gas temperature at the outlet of the cooling tower 3 is about 70.degree. C. Then, ammonia is added to the waste gas and the mixture is introduced into a reactor 7 where it is irradiated with electron beams. SO.sub.x and NO.sub.x in the waste gas are oxidized by irradiation with electron beams to form sulfuric acid and nitric acid, respectively, which further react with ammonia to form dust particles such as ammonium sulfate and ammonium nitrate. The waste gas containing the resulting dust particles is passed through a duct and introduced into a by-product dust collector where the dust is separated from the gas and then the treated gas is released into the atmosphere.
When waste gas is irradiated with electron beams, X-rays are partially generated by bremsstrahlung. As is well known, the rate of generation of X-rays by bremsstrahlung is quite small, but, since the range of the generated X-rays is longer than that of electron beams, the X-rays must be shielded by means, for example, of lead or concrete.
FIG. 2 illustrates the structure of a typical irradiation chamber of an apparatus for carrying out the waste gas treating method. In this apparatus, the electron beam irradiation sections 8' of the electron beam accelerator and the reactor 7 are installed in an irradiation chamber 13 made of a shielding material, for example, concrete, as shown in FIG. 2, in order to provide a shield against X-rays resulting from the irradiation with electron beams. A maze (zigzag passage) 15 is defined by the shielding materials, and ducts 5' and 9' for introducing waste gas into the reactor 7 and discharging the gas irradiated with electron beams from the reactor 7 are disposed zigzag fashion along the maze 15, thereby allowing electron beam irradiation to be carried out with a shield provided against X-rays. The maze 15 is generally arranged in such a manner that the passage is bent two or three times at substantially right angles, thereby preventing X-rays from leaking out of the irradiation chamber 13.
X-rays that penetrate into the shielding material decay therein but some of them are reflected. The intensity of the reflected X-rays is exceedingly weak, i.e., one/hundredths to one/thousandths of that of the X-rays before reflection. Accordingly, it is possible to provide an effective shield against the X-rays by means of a maze having a structure in which the passage is bent two or three times at substantially right angles.
The waste gas that contains dust particles of a by-product produced by the irradiation with electron beams is introduced into the by-product dust collector 10 outside the irradiation chamber 13 through the maze-like duct 9 having such a structure that the duct is bent two or three times at substantially right angles. Inside this maze-like duct, particularly the portions which are bent at substantially right angles, adhesion and deposition of dust are found to occur, and these lead to an increase in pressure loss of the waste gas being treated and disturbance of stable operations.